A variety of implantable medical devices (IMDs) for delivering a therapy, monitoring a physiological condition of a patient or a combination thereof have been clinically implanted or proposed for clinical implantation in patients. Some IMDs may employ one or more elongated electrical leads carrying stimulation electrodes, sense electrodes, and/or other sensors.
IMDs may deliver therapy to and/or monitor conditions of a variety of organs, nerves, muscle or tissue, such as the heart, brain, stomach, spinal cord, pelvic floor, or the like. Some IMDs, such as cardiac pacemakers or implantable cardioverter defibrillators (ICDs) monitor a patient's heart activity by sensing cardiac electrical signals to detect an abnormal rhythm. Pacemakers and ICDs may provide therapeutic electrical stimulation to the heart of the patient via electrodes carried by a medical electrical lead coupled to the pacemaker or ICD. The electrical stimulation may include pacing pulses to address abnormal cardiac rhythms such as bradycardia and ventricular tachycardia or cardioversion/defibrillation shocks for treating malignant forms of ventricular tachycardia and ventricular fibrillation. The reliability of an IMD in delivering electrical stimulation pulses to treat abnormal rhythms and sensing electrical physiological signals for monitoring a patient depends at least in part on the integrity of the insulation and the electrical conductors of the medical electrical lead that carries electrodes used for delivering the therapeutic stimulation pulses and for sensing physiological signals.